Which nails are right for the job?

I have been looking for nails for my Hitachi nailer, I purchased 3" (10d) nails and 3 1/2"(16d) nails for general framing. I have always used 6d CC sinkers for 7/16 decking(OSB). I am having trouble finding 2"(6d) nails for my gun locally. I can find them online at places like the nail zone. Locally I am told everyone uses the 2 3/8" nails, which is between a 7d and 8d nail. That seems too long for basic decking nails, or is it. What do you guys use? Also, almost all I can find is in bright finish for my nailer, no cement coated. Is that okay.
What about ring shank? Should I use ring shank instead of smooth?
The more I look, the more unsure I am.